YAVORIV, UKRAINE - APRIL 30, 2015: A Ukrainian soldier participates in a mock house raid, a component of military training directed by the U.S. Army's 173rd Airborne Brigade as part of Operation Fearless Guardian at the Yavoriv training center near Yavoriv, Ukraine. Around 300 American soldiers are training an equivalent number of Ukrainians during each of three eight-week programs to improve their ability to combat Russian-backed rebels in the country's east. CREDIT: Brendan Hoffman for The New York Times